Mormon documents the rise to power of the Gadiantons as the majority Nephite party. This rule gives them control over the resources that allow them to increase their wealth. Their political dominance also protects them from the legal consequences of “their murders, and their plunderings, and their stealings.” Each term is highly pejorative, which, not surprisingly, is exactly how Mormon saw them. However, from the Gadianton/Nephite perspective, these terms might be recast as military conquests. The “murders” would therefore become death in wars of conquest, while “plunderings and stealings” were the tribute assessed on the conquered.
As I hypothesized with the Anti-Nephi-Lehies, Mormon may include ritual human sacrifice in what he calls “murders.” There is no corroborating evidence for this hypothesis in the text; but since it was an aspect of the war cult that otherwise fits this method of accumulating wealth, the possibility may exist that this heinous practice was being instituted among the apostatizing Nephites. (See commentary accompanying Alma 17:14, 50:21, and Helaman 6:17.)